/**
 * Copyright (c) 2010 by Kevin Bierhoff.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *    1. Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *    2. Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *    3. Neither the names of the authors nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ''AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package com.googlecode.syper.javasyp.checker;

/**
 * @author kevin
 *
 */
public enum PermKind {
	EXCL {
		@Override
		public boolean isStrongerThan(PermKind other) {
			return true;
		}

		@Override
		public boolean isModifying() {
			return true;
		}

		@Override
		public PermKind weaken(PermKind owned) {
			return owned;
		}

		@Override
		public PermKind join(PermKind other) {
			return other;
		}
	},
	IMM {
		@Override
		public boolean isStrongerThan(PermKind other) {
			return other != EXCL;
		}

		@Override
		public boolean isSymmetric() {
			return true;
		}

		@Override
		public PermKind weaken(PermKind owned) {
			return IMM;
		}

		@Override
		public PermKind join(PermKind other) {
			return other == null ? null : this;
		}
	};

	public static final PermKind[] EMPTY_PERM_KIND_ARRAY = new PermKind[0];

	/**
	 * Safe version of {@link #valueOf(String)} that returns <code>null</code>
	 * if given identifier unknown instead of throwing
	 * @param identifier
	 * @return <code>null</code> if given identifier unknown, corresponding
	 * enum value otherwise
	 */
	public static PermKind valueOrNull(String identifier) {
		try {
			return PermKind.valueOf(identifier);
		} catch (IllegalArgumentException e) {
			return null;
		}
	}

	public abstract boolean isStrongerThan(PermKind other);

	public boolean isSymmetric() {
		return false;
	}

	public boolean isModifying() {
		return false;
	}

	/**
	 * Indicates if the permission protects against modification
	 * @return {@code true} if permission protects against modification,
	 * {@code false} otherwise
	 */
	public boolean isProtection() {
		return true;
	}

	/** Weaken argument for unpacking receiver */
	public abstract PermKind weaken(PermKind owned);

	/** Approximate receiver and argument */
	public abstract PermKind join(PermKind other);
}
